Development of information and communication technology leads to an exchange of various types of data, and it is becoming a big problem how to ensure privacy (safety) of the data to be transmitted. Cryptographs currently used for ensuring privacy of data, such as RSA, base safety on cryptanalysis time by a computer based on computational complexity. However, further improvement in computational ability of a computer may allow easy cryptanalysis of RSA or the like.
In contrast, a quantum key distribution (QKD) system for achieving data privacy based on a physical law of light is known. The quantum key distribution system (quantum cryptographic communication system) is a system capable of detecting eavesdropping on a communication channel by handling a quantum state of light as data representing zero or one. The quantum key distribution system is expected as a cryptographic method for achieving information-theoretical safety that does not base safety on cryptanalysis time by a computer.
Generally in a quantum communication device used for a quantum key distribution system, error correcting (EC) processing and privacy amplification (PA) processing are performed.
However, conventional techniques do not take into consideration a difference in processing speeds between the error correcting processing and the privacy amplification processing, and thus cryptographic key data cannot be generated efficiently.